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I'm thinking about air shield that can protect man from flying arrows, bullets, etc.
I did some research about bulletproof vests and it turned out that many of them were made of hard materials or gelatin. So I thought just creating a shield by collecting air molecules and making a metal-like structure with them(so it's practically solidifying the air). Would this be possible? And another thing - will that be transparent?

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    $\begingroup$ Armor and gelatin are focused on stopping the projectile. Air shield could just deflect arrow which require less energy. Bullet deflection is much harder since it significantly smaller and faster than arrow. The possibility to stop a projectile is very different than deflect it so there are 2 questions with different answers $\endgroup$ – ADS Jun 17 '17 at 9:41
  • $\begingroup$ Please note that the science-based tag is a more stringent form of the reality-check tag; using both is redundant. Also, please try to avoid having these tags be the only tags on a question. I've edited the tags; if you disagree with my selection feel free to change them. $\endgroup$ – Frostfyre Jun 17 '17 at 12:02
  • $\begingroup$ Are you talking about fusing the molecules? If so then why are you bothering with a shield? You can just burn your enemies in nuclear fire. Even if you "only" have enough energy to compress your air until it becomes solid it will heat up to the point where it would be easier and safer to incinerate your enemies rather than shield yourself with it. (projectiles might melt/boil as they pass through but still have enough momentum to hit you). $\endgroup$ – Taha Attari Jun 17 '17 at 13:31
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You are asking for science-based, so the answer is "no" to the first question and "yes" to the second (since it doesn't exist).

Air is a mixture of simple elements (mainly Nitrogen and Oxygen) that, at normal temperature, are in gas form.

There is no (science-based) way to "collect the molecules" short of solidifying air near Absolute Zero temperature.

The best you can effectively do is have some form of focused sound waves, but that would probably be to thin or too weak to be an efficient shield. Such limitations might conceivably be overcome in future, but I didn't go through the work of computing the energy required. Such a shield (akin to the "sonic wall") would be almost invisible.

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  • $\begingroup$ No need to go near absolute zero. For example CO2 can be solid under normal pressure and relatively high temperatures of almost 200K. $\endgroup$ – Mołot Jun 17 '17 at 8:32
  • $\begingroup$ @Mołot; it all depends on how You interpret "air shield" in requester phrasing. CO2 is very scarce in "air", main component is Nitrogen that freezes at 63K which is nearer to absolute zero than room temperature (Oxygen goes even lower). Thus if You interpret the phrase as "with something pulled out from air" Your objection is valid. I chose a more literal interpretation. Requester will decide. $\endgroup$ – ZioByte Jun 17 '17 at 9:15
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You could look into some carbon nano-structures - these tend to be extremely strong and can have interesting properties such as transparence. If you can handwave a way to arrange these nano-structures on the spot out of carbon in the air this might work for you. Unfortunately the amount of carbon in the air is probably not high enough to make much of a shield.

The better solution was mentioned in comments: don't try to stop the projectile, but rather deflect it. Ideally this 'shield' would be placed as far away as possible, as small changes in trajectory far away can have much larger impact than large changes much closer to the target. Finally, the type of projectile will make a very large difference in the effectiveness of this 'wind shield'. A large, slow moving projectile like an arrow will be greatly affected by the wind, and this could be a legitimate protection. A smaller, fast moving projectile like a bullet would need to be subjected to the wind for much longer than it would realistically take to pass by your shield to have any real effect.

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You can make diamond from the carbon in the air.

Air contains a fair amount of carbon, this is what plants primarily use for structure. If you can gather air, derive and isolate the carbon then control how it bonds with itself, you can make a lot of really cool materials (including diamond). You can also combine it with airborne water to make petroleum products.

So yeah, you can pull diamonds out of the air. As far as making it into whatever shape you choose, you might use another question.

At sufficient pressure air would stop your projectiles without a chemical change. This could require a lot less air, unless there is a lot of carbon in the atmosphere. Maintaining the field need not require energy unless pressure is lost.

This would be many times more effective if the air were superheated after being trapped.

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  • $\begingroup$ With the advantage of interesting side effects when the pressure vessel of the shield is cracked. $\endgroup$ – AlexP Jun 17 '17 at 9:41
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    $\begingroup$ The issue with the first part is that (on earth at least) air has a ridiculously small amount of carbon (like 0.4%) $\endgroup$ – Taha Attari Jun 17 '17 at 13:25
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    $\begingroup$ @TahaAttari: 0.04% carbon dioxide; and carbon dioxide is about 70% oxygen... $\endgroup$ – AlexP Jun 17 '17 at 13:36
  • $\begingroup$ It's enough for plants, wasn't sure of the time frame $\endgroup$ – user39453 Jun 17 '17 at 18:29

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